Two Times a Charm: Recycling Acquaculture Water on Olive Trees

To help farmers and ranchers conserve water, especially precious in the arid Southwest, SARE-funded researchers at the University of Arizona combined shrimp and olive production to test whether they could produce two commodities using less water and commercial fertilizer.

“Arizona farmers are under a lot of economic and environmental pressure to be more efficient with the water they use to produce crops,” said project leader Kevin Fitzsimmons, a researcher at the University of Arizona. “We wanted to show how to pair crops with aquaculture, running water through fish or shrimp first, then putting it on their field crops.”

Not only can farmers reap a double benefit by using aquaculture pond or tank water to irrigate crops, but they also gain extra nutrients from fish waste. Fitzsimmons and his research team set out to find out how much benefit that effluent can provide as crop fertilizer. On a Gila Bend, AZ, shrimp farm, the team designed a plot of 120 olive trees, spaced along 10 rows. From the shrimp pond, they irrigated olive saplings and compared canopy height and trunk circumference to a set of trees watered from a well.

Effluent-treated trees grew larger than well-watered trees, supplying saplings with 1.6 to 5.6 kilograms of nitrogen per row from the shrimp waste. In the second year, they met the full nitrogen recommendation for olive trees. “A major point is that we're using the nitrogen and phosphorus in the waste from the shrimp to replace the N and P fertilizers that farmers would otherwise have to buy,” Fitzsimmons said. “We supplied close to 100 percent of nutrients needed for the trees at that size.”

Gary Wood, the shrimp farm's owner, continues to irrigate olive trees as well as durum wheat fields from his shrimp pond, which is fed by well water. Wood, who also received a farmer/rancher grant from SARE to develop direct markets for his Desert Sweet Shrimp, calls the system “a classic example of environmental synergy.”

Fitzsimmons also tested shrimp pond sludge—shrimp waste that settles to the bottom—on tomato plots at the university's Environmental Research Lab. The tomatoes amended with sludge in Fitzsimmons' project produced significantly more fruit than the tomatoes in the control plot with unamended soil: 141 grams of fruit per plant compared to 39 grams in the control plants. Through field days, Fitzsimmons' team publicized their results and, since then, close to a dozen Arizona crop farmers are trying to integrate fish and shrimp farming into their systems.